1) Field of the Invention
The present invention relates to a formwork system for use in slip form casting central cores of high rise buildings.
2) Description of the Prior Art
As is well known in the construction industry, the central core of a high rise building is conventionally constructed by a slip form casting process by which successive stages of the core are formed, typically with each stage corresponding to one story of the building. The central core forms the principal structure of the building from which the individual floors are cantilever mounted. It typically acts as the structure for containing lifts, fire escape stairs, and service ducts.
When each story is cast, it is conventional to form along the outer side of the core a rebate into which will be cast the inner end of a floor slab at that level. The rebate is defined by a form of appropriate cross-section attached to the inside face of the main formwork. With the existing system, accommodation has to be made for reinforcement which needs to extend from the core at the level of the rebate in order to subsequently tie into the reinforcement for the cast floor slab. Principally, the reinforcement is cast into the core, but because of the presence of the main formwork and rebate form during casting, the part of the reinforcement which is to project from the core needs to be bent to lie along the interior of the rebate form. For this purpose, the rebate form is of hollow or box-like construction so as to receive the bent lengths of reinforcement. The actions of bending the reinforcement to set the reinforcement into the interior of the rebate form for casting and then subsequently straightening the reinforcement after casting to permit stripping of the reinforcement from the rebate form and to set lie reinforcement in the correct configuration for use, are quite time-consuming. Moreover the bending and subsequent straightening can lead to reduced ductility of the reinforcement which is undesirable and difficulties are sometimes encountered in ensuring that the ductility remains within prescribed limits.